Gear pump for pumping abrasive well fluid

ABSTRACT

A gear pump is configured for pumping abrasive fluids from a well. The gear pump includes an electrical motor that is sealed within a motor housing and submersed with the pump. The gear pump has a drive shaft that rotates a drive member, which in turn rotates a driven gear. The gear pump has intake chamber leading to an intake side of the drive and driven gears and a discharge chamber extending from the discharge side. One of the gears has metal teeth while the other has elastomeric teeth.

FIELD OF THE INVENTION

This invention relates in general to well pumps, and in particular to alow volume positive displacement pump for pumping abrasive well fluid.

BACKGROUND OF THE INVENTION

Centrifugal pumps are commonly used in oil well production for producinglarge volumes of fluid. A centrifugal pump assembly comprises a downholeelectrical motor, a pump made up of a plurality of stages, each stagehaving an impeller and diffuser, and a seal section located between themotor and pump. The seal section equalizes the pressure of lubricantwithin the motor with the hydrostatic pressure of well fluid on theexterior. If the well produces a significant amount of sand, to reducewear, some of the thrust and radial bearings in the stages can be formedof a hard, wear resistant material, such as tungsten carbide.

Some wells require only fairly low flow rate pumps. For example,dewatering coal bed methane wells can be done with a small centrifugalpump but small centrifugal pumps are not particularly efficient. Also,if the well fluid contains abrasive particles, providing centrifugalwell pumps with hard, wear-resistant components to resist the abrasivewear is expensive.

SUMMARY OF THE INVENTION

In this invention, a positive displacement pump is utilized for lowvolume wells having abrasive fluid. The positive displacement pump ispreferably of a type having a driven member with lobes that intermeshwith lobes of a drive member, such as a gear pump. An electric motorrotates the drive member, causing well fluid on an intake side to flowbetween the lobes of the drive and driven members to a discharge side.The intake leads to the exterior of the pump and is submersed in thewell fluid. The discharge is connected to a conduit leading to thesurface of the well.

To resist abrasive wear, one of the members has lobes or teeth formed ofa hard, wear-resistant metal. The other member has lobes or teeth formedof an elastomeric material. The elastomeric material deflects whencontacted by abrasives in the well fluid, reducing wear on the metalteeth. Preferably the drive and driven members comprise gear teeth.

In one embodiment, the drive and driven members are located within acavity of a plate of a uniform thickness. The plate is sandwichedbetween a motor housing and a manifold housing. The thickness of theplate is the same as the thickness or axial dimension of each of thedrive and driven members. The flow rate can be changed by increasing thedimension of the drive and driven members. The plate can be readilyinterchanged with a plate having a thickness to match the thickness ofany drive and driven members selected. The motor and manifold areinterchangeable with different thicknesses of plates.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is schematic sectional view illustrating a gear pump constructedin accordance with this invention installed within a well.

FIG. 2 is an enlarged vertical sectional view of the gear pump of FIG.1, taken along the line 2-2 of FIG. 4.

FIG. 3 is an enlarged vertical sectional view of the gear pump of FIG.1, taken along a vertical plane 90 degrees from the sectional plane ofFIG. 2.

FIG. 4 is a sectional view of the gear pump of FIG. 1, taken along theline 4-4 of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, a well having a casing 11 is illustrated. Well 11is of a type that that requires pumping at a fairly low flow rate andmay contain abrasive material within the well fluid. For example, well11 may be a coal bed methane well that requires dewatering.

A string of conduit or tubing 13 is shown suspended within casing 11. Apositive displacement pump assembly, preferably a gear pump 15, issuspended from the lower end of tubing 13. Gear pump assembly 15 has anintake 17 submersed within the well fluid for pumping the well fluid uptubing 13 to the surface.

Referring to FIG. 2, pump assembly 15 includes a submersible electricalmotor 19. Electrical motor 19 is located within a motor housing 21 thatis sealed from the well fluid, and forms part of the housing assembly ofpump assembly 15. Motor housing 21 has a bottom 21 a, a top 21 b, and acylindrical sidewall 21 c. Motor 19 may be of a variety of types but ispreferably an AC motor with a stator 23 having a central opening forreceiving a rotor 25. Rotor 25 causes a drive shaft 27 to rotate whenstator 23 is energized. Electrical power is supplied to motor 19 by apower cable (not shown) that extends downward from the surface. Driveshaft 27 is supported by a lower bearing 29 on motor housing bottom 21 aand a radial bushing within a depending tubular portion of top 21 b. Inthis embodiment, drive shaft 27 is located on the axis of motor housing21.

The housing assembly for pump assembly 15 also includes a pump baseplate 33, which is mounted on motor housing top 21 b. Pump base plate 33is preferably a solid, metal plate such as stainless steel, that hasbeen hardened and is resistant to wear where exposed to the abrasivefluid well. Plate 33 has a flat lower side and a flat upper side, thesides being parallel to each other to define a uniform thickness forplate 33. Plate 33 is separated from housing top 21 b in this embodimentby a gasket 34 to prevent leakage.

As shown clearly in FIG. 4, plate 33 has a closed cavity formed withinit, the cavity having an intake portion 35, a discharge portion 37, adrive gear portion 39 and a driven gear portion 41. Portions 35, 37, 39and 41 join each other to form general cross shape with rounded ends. Inthis embodiment, intake cavity portion 35 and discharge cavity portion37 are semi-circular. Similarly, drive gear cavity portion 39 and drivengear cavity portion 41 are semi-circular.

A drive gear 43 is rotatably mounted within drive gear cavity 39. Drivegear 43 is a gear member that has a plurality of lobes or teeth 45spaced around its circumference. Drive gear 43 is preferably formed of ahard wear-resistant metal, such as stainless steel. Drive gear 43 isrigidly secured to drive shaft 27 by a key for rotation therewith.

A driven gear 47 is located adjacent drive gear 43. Driven gear 47 alsohas a plurality of lobes or teeth 49 spaced around its periphery. Teeth45 intermesh with teeth 49 so that rotation of drive gear 43 causesdriven gear 47 to rotate. Driven gear 47 is rigidly mounted to a drivenshaft 51 that is free to rotate. As shown in FIG. 3, driven shaft 51 hasa lower end that rotatably fits within a receptacle 53 containing abushing 55. Bushing 55 seals drive shaft 27 and bushing 31 seals drivenshaft 51, preventing leakage of well fluid into motor housing 21. Drivenshaft 51 is parallel to drive shaft 21.

In this embodiment, drive and driven gears 43, 47 are identical in size,but driven gear 47 is formed of a resilient elastomeric material.Alternately, driven gear 47 could be formed of a hard, wear resistantmetal and drive gear 43 formed of an elastomeric material. Moreover,both drive gear 43 and driven gear 47 could be formed of the samematerial, either elastomer or metal, particularly if the well fluid isnot very abrasive.

Referring to FIGS. 2 and 3, the housing assembly for pump assembly 15also includes a manifold housing 57, which fits on top of pump baseplate 33 and is separated by a sealing gasket 59. Manifold housing 57has a drive shaft receptacle 61 that receives the upper end of driveshaft 27. A bushing 63 is located within receptacle 61 to serve as aradial support bearing. Manifold housing 57 also has a driven shaftreceptacle 65 that is adjacent and parallel to drive shaft receptacle61. Driven shaft receptacle 65 has a bushing 67 for rotatably receivingthe upper end of driven shaft 51. Bolts (not shown) extend from manifoldhousing 57 through base plate 33 and into threaded receptacles in motorhousing 21, clamping base plate 33 between manifold housing 57 and motorhousing 21.

As shown in FIG. 2, manifold housing 57 has an intake port 69 that leadsfrom the exterior of manifold housing 57 downward and inward intoregistry with intake cavity portion 35 (FIG. 4). Manifold housing 57 hasa discharge port 71 that leads outward and is in registry with dischargecavity portion 37 (FIG. 4). Discharge port 71 preferably leads throughan upper end 73 that contains threads or structure for securing pumpassembly 15 to the lower end of tubing 13.

In operation, electrical power is supplied to motor 19, which causesshaft 27 to rotate drive gear 43 (FIG. 4). Drive gear 43 rotates drivengear 47, and the intermeshing engagement of gears 43, 47 draws wellfluid through intake port 69 into intake cavity 35 (FIG. 4). Therotating engagement of gears 43, 47 forces the well fluid into dischargecavity 37, and from there through discharge port 71 up tubing 13.Abrasive particles in the well fluid may temporarily embed in theresilient elastomeric driven gear 47, thereby enabling the particles topass through the pump without damage to either gear 43 or 47.

The flow rate is a function of the axial dimension of drive and drivengears 43, 47. The flow rate increases as the axial dimension orthickness of gears 43, 47 increases. In addition to making gears 43, 47with different thicknesses, stacking multiple drive gears 43 upon eachother, and multiple driven gears 47 upon each other is another manner inwhich the thickness can be increased. Electrical motor 19 would have thecapacity to accommodate gears 43, 47 of various thickness. Also, motorsof smaller and larger capacity could readily bolt to pump base plate 33.Manifold housing 57 would be operable for a wide variety of flow rates.Pump base plate 33 should have a thickness that matches the thickness ofdrive and driven gears 43, 47, thus it would differ depending upon theflow rate of the pump.

Motor housing 21, base plate 33 and manifold housing 57 are modularcomponents fastened together by bolts. The modularity allows themanufacturer or a distributor to easily provide pump assemblies withdifferent flow rates using the same motor 19 and manifold housing 57,but different gears 43, 47 and base plates 33.

The invention has significant advantages. The downhole gear pump has ahigher efficiency than a small centrifugal pump for low volumeproduction. Using an elastomeric gear running against a hard metal gearreduces wear caused by abrasive particles in the well fluid. Expensivehardened components are not required for abrasive well fluids. The pumpis modular and has components that can be readily interchanged to varythe capacity of the pump.

While the invention has been shown in only one of its forms, it shouldbe apparent to those skilled in the art that it is not so limited butsusceptible to various changes without departing from the scope of theinvention.

1. A well pump apparatus for pumping abrasive fluids from a well,comprising: a housing assembly for submersion in well fluid in a well;an electric motor sealed within the housing assembly against the wellfluid; a drive shaft rotated by the motor and located within the housingassembly; a drive member located within the housing assembly andoperatively coupled to the drive shaft for rotation therewith, the drivemember having a plurality of lobes spaced around an axis of the driveshaft; a driven member rotatably mounted in the housing assembly next tothe drive member, the driven member having a plurality of lobes thatintermesh with the lobes of the drive member; an intake chamber in thehousing assembly leading from an exterior of the housing assembly to anintake side of the drive and driven members for flowing well fluid intocontact with the drive and driven members; a discharge chamber in thehousing assembly extending from a discharge side of the drive and drivenmembers to the exterior of the housing assembly for discharging the wellfluid passing through the drive and driven members while rotating; andthe lobes of one of the members having metal surfaces, and the lobes ofthe other member having elastomeric surfaces to reduce wear due toabrasive particles in the well fluid passing through the drive anddriven members;.
 2. The apparatus according to claim 1, wherein themember having the lobes with elastomeric surfaces comprises anelastomeric sleeve mounted on a metal core.
 3. The apparatus accordingto claim 1, wherein the lobes of the drive and driven members comprisegear teeth.
 4. The apparatus according to claim 1, wherein each of thedrive and driven members has an axial dimension that is the same, andwherein the housing assembly further comprises: a base plate having athickness that is the same as the axial dimension of the drive anddriven members, the plate having cavities formed therein for definingthe intake and discharge chambers.
 5. The apparatus according to claim1, wherein the housing assembly comprises: a motor housing enclosing themotor; a manifold housing having an inlet for the intake chamber and anoutlet for the discharge chamber; and a base plate sandwiched betweenthe motor housing and the manifold housing, the plate having cavitiesformed therein for defining the intake and discharge chambers.
 6. Theapparatus according to claim 5, wherein each of the drive and drivenmembers has an axial dimension that is the same, and wherein the platehas a thickness that is the same as the axial dimension of the drive anddriven members.
 7. The apparatus 6, wherein the plate is releasablyclamped between the motor housing and the manifold housing to enable thedrive and driven members and the plate to be interchanged with drive anddriven members of different axial dimensions and plates of differentthicknesses.
 8. The apparatus according to claim 5, wherein the plate isformed of a hard, wear-resistant material.
 9. The apparatus according toclaim 1, wherein the metal surfaces on the lobes of said one of themembers comprises a hard, wear resistant material.
 10. A well pumpapparatus, comprising: a string of conduit suspended in a well; and agear pump having a submersible electric motor, an intake leading to theexterior of the gear pump for drawing well fluid from the well and adischarge coupled to the conduit for pumping the well fluid through theconduit to the surface.
 11. The apparatus according to claim 9, whereinthe gear pump comprises: a drive member driven by the electric motor andhaving a plurality of lobes; a driven member having a plurality of lobesthat intermesh with and are driven by the lobes of the drive member; andwherein the lobes of one of the members are formed of metal and thelobes of the other of the members are formed of an elastomeric material.12. The apparatus according to claim 11, wherein each of the drive anddriven members has an axial dimension that is the same, and wherein thegear pump further comprises: a plate having a uniform thickness that isthe same as the axial dimension of the drive and driven members, theplate having cavities formed therein for defining intake and dischargechambers that receive the drive and driven members.
 13. The apparatusaccording to claim 9, wherein the gear pump comprises: a motor housingenclosing the motor; a manifold housing defining the intake anddischarge; and a base plate of uniform thickness sandwiched between themotor housing and the manifold housing, the plate having cavities formedtherein for defining intake and discharge chambers, the plate beinginterchangeable with plates of different thicknesses.
 14. The apparatusaccording to claim 13, wherein the plate is formed of a hard,wear-resistant material.
 15. A method of pumping well fluid from a well,comprising: suspending a gear pump and submersible electric motor in thewell; and supplying electrical power to the motor to cause the gear pumpto draw well fluid therein and pump the well fluid to the surface. 16.The method according to claim 15, further comprising: providing the gearpump with drive and driven members having intermeshing lobes, the drivemember being driven by the electric motor; and wherein the lobes of oneof the members are formed of metal and the lobes of the other of themembers are formed of an elastomeric material.